Prior art automobiles and motorcycles have incorporated a device in which a closed air chamber is contained within a cushion unit (a shock absorber), and this air chamber is adapted to give a required spring constant when filled with high pressure air, the length of the cushion unit being changed by injecting or exhausting high pressure air to adjust vehicle height. In vehicles provided with such a device, exhaust air from a compressor carried on the vehicle is fed to the air chamber of the unit, for example through a solenoid valve, so as to expand the unit. To contract the unit, the high pressure air in the air chamber is exhausted to atmosphere through the other solenoid valve.
Japanese Utility Model Publication No. 19997/1976 discloses a mechanism by which a driver can obtain a desired vehicle height by air injection into or air exhaust from a suspension unit via a compressor for adjusting the vehicle height, the pressure applied to the suspension being measured by a pressure gauge. The reference does not disclose that air is evacuated through an air outtake port and that air pressure of a tire can be adjusted by utilizing a pressure gauge for adjusting vehicle height.
While the compressor in prior art devices may be used for supplying air to the tire, removal of air from the tire by direct bypass from the compressor requires a system separate from the vehicle height adjusting device. Accordingly, it cannot check the air pressure of the tire, and such air pressure must therefore be measured by means of a separate air gauge.